Dementia is one of the most greatly feared diseases of old age. Its personal and social consequences are formidable. So far, medicines have proved useful in some individuals once they have developed the condition, but none has been shown conclusively to prevent its onset.

Now, though, an American study* provides some indirect evidence that including omega-3 oils in your diet might help protect you against the disease.

Omega-3 oils are found especially in oily fish such as salmon, herring and mackerel, and to a lesser extent in other seafood, walnuts, flaxseed, canola oil and meat from grass-fed animals.

The study looked at a range of different nutrients in the diets of 1200 people aged 65 or more, and also at the amount of “amyloid-ß” in their blood. Levels of amyloid-ß are higher in some people who go on to develop dementia. The researchers argued that if its level could be lowered then those individuals would be at a lower risk of developing dementia.

This may seem a rather indirect approach, but dementia is hard to study directly. Much previous work has been based on self-reporting by the subjects; this is difficult in those without dementia and even more so in those who have the condition. Using a marker for dementia such as amyloid-ß therefore has advantages.

Out of all the nutrients the researchers looked at – which included vitamins and other types of oil – the only one associated with lower levels of amyloid-ß was omega-3 oil. The subjects who consumed the most omega-3 oil in their diet had significantly lower amounts of amyloid-ß. That suggests omega-3 oil may help prevent dementia. However, only long-term trials over many years will tell whether they are right.

This study on its own is not enough evidence to make a universal recommendation that everyone should consume omega-3 oil to prevent dementia.

But omega-3 oil is already recommended by health professionals as it is an essential nutrient needed by your body and it provides strong, proven protection against heart disease and a range of other serious conditions. If it protects you from dementia as well, that is an added bonus.